1. Field of the Invention
The present invention relates to a semiconductor device and a method of manufacturing the same. More specifically, the present invention relates to a wiring structure of a capacitor including a metal oxide dielectric material.
2. Background Information
A FeRAM (Ferroelectric Random Access Memory) is a high-speed nonvolatile memory using a hysteresis characteristic of a ferroelectric material. The FeRAM is outstanding in that it has the ability to write as fast as a DRAM (Dynamic Random Access Memory), consume little power, and so forth.
Further, in case of forming a capacitor using a ferroelectric material, i.e. a metal oxide, annealing at high temperature (600 to 800 degrees C.) in an oxygenated environment is required for sintering the ferroelectric material and recovering the characteristic of the ferroelectric material after etching. Taking this into account, both of two electrodes contacting the ferroelectric material are made of a noble metal such as platinum (Pt), iridium (Ir), and so forth, which has high oxidation resistance. In particular, platinum (Pt) has high stability and workability, so that it is most often used in the electrodes.
For example, a wiring structure of a ferroelectric capacitor having platinum electrodes is shown in Japanese Laid Open Patent Publication No. 10-256503, which is hereby incorporated by reference. According to the wiring structure as disclosed in Publication No. 10-256503, a main wiring material is aluminum (Al) and a main electrode material is platinum (Pt). In general, aluminum (Al) and platinum (Pt) are known to overreact with each other. Such overreaction may cause voids on the aluminum wirings. Moreover, if the reactions between the aluminum (Al) and platinum (Pt) are excessive, the aluminum wirings may break away. In this respect, the wiring structure as disclosed in Publication No. 10-256503 has a protective layer on the capacitor electrode in order to prevent the aluminum (Al) and platinum (Pt) from overreacting with each other.
As described above, platinum (Pt) used as an electrode material of a ferroelectric capacitor overreacts with aluminum (Al), which is a common wiring material. This overreaction causes voids on the aluminum wirings. Moreover, if the reactions between the aluminum (Al) and platinum (Pt) are excessive, the aluminum wirings may break away. For this sake, generally, a barrier film like titanium nitride (TiN) film is arranged between the platinum electrode and the aluminum wiring. However, since the crystal structure of titanium nitride (TiN) is a columnar crystal structure, aluminum atoms can easily diffuse through intergranular spaces of the TiN crystal grains. Thus, uniformly forming a titanium nitride film at the interface between the platinum electrode and the aluminum wiring does not provide a sufficient barrier effect.
The wiring structure according to Publication No. 10-256503 has a protective layer for preventing possible reactions between the platinum electrode and the aluminum wiring of the capacitor. The protective layer is constructed with a barrier layer, a stopper layer, and an adhesion layer. However, when the protective layer is formed, it is integrated with the capacitor electrode at the upper part of this capacitor electrode. This makes the capacitor electrode thicker, which in turn makes the whole structure of the capacitor thicker.
Furthermore, according to Publication No. 10-256503, an etching process is carried out for forming a contact hole to connect electrically the capacitors electrodes and the wirings after forming the protective layer. However, a ferroelectric film can be damaged in this etching process. In order to recover the characteristic of the ferroelectric film, annealing at high temperature in an oxygen environment is needed. However, this annealing can cause oxidation of the protective layer which has already been formed. This oxidation may cause deterioration in the electrical characteristic of the protective layer and abruption of the protective layer.
Moreover, in Publication No. 10-256503, with respect to the capacitor structure of a stack type, the protective layer is formed only for the upper electrode of the capacitor. However, in a structure where both of the upper and lower electrodes of the capacitor are electrically pulled out upward by contacts, a protective layer should also be formed for the lower electrode of the capacitor. Publication No. 10-256503 does not disclose forming a protective layer for the lower electrode.
In view of the above, it will be apparent to those skilled in the art from this disclosure that there exists a need for an improved semiconductor device and an improved method of manufacturing the same. This invention addresses this need in the art as well as other needs, which will become apparent to those skilled in the art from this disclosure.